1. Field of the Invention
The present invention relates to a perforating machining method based on the use of a laser beam, which makes it possible to form invisible minute through-holes through a workpiece by radiating the laser beam onto the workpiece. In particular, the present invention relates to a perforating machining method based on the use of a laser beam, which makes it possible to form, for example, a weak portion for an air bag of an air bag system to be installed to an automobile.
2. Description of the Related Art
In recent years, the air bag system has been widespread, for example, for vehicles such as automobiles. The air bag system is provided with an air bag which functions as an air-expandable bag to be used for an apparatus for absorbing the shock. The air bag is folded, and it is accommodated in an accommodating air bag module. When the collision of the vehicle is detected by a sensor, the air bag is instantaneously expanded by the gas supplied from a gas generator. Thus, the air bag functions as a cushion to absorb the shock applied to a driver or a passenger.
The air bag is installed in a state of being hidden in an interior part such as a steering wheel cover and an instrument panel. When the air bag is expanded, then a door panel for developing the air bag is opened by force, and the air bag is exposed to the outside of the accommodating air bag module.
In this arrangement, in order to reliably open the door panel, for example, a weak portion for the air bag is formed with a predetermined machining pattern composed of grooves, holes and the like.
As a method for forming the weak portion for the air bag, for example, Japanese Laid-Open Patent Publication No. 58-16784 discloses a method for perforating and machining a workpiece by providing a photodetector on the side of a surface opposite to a machining surface of the workpiece, and sensing, with the photodetector, a laser beam passed through a through-hole of the workpiece.
Japanese Laid-Open Patent Publication No. 8-282420 discloses a method for forming a weak portion by partially forming grooves with a laser beam for a door panel of an automobile interior cover at an opening for developing an air bag.
Japanese Laid-Open Patent Publication No. 10-85966 discloses a method for forming a linear weak portion based on the use of radiation of a controllable pulse-shaped laser beam.
However, in the case of the technical concept disclosed in Japanese Laid-Open Patent Publication No. 58-16784 concerning the conventional technique described above, the following inconvenience arises. That is, the diameter of the through-hole formed by the perforating machining is increased due to the influence of the delay time until the radiation of the laser beam is actually stopped after the laser beam is detected with the photodetector. The bored through-hole is visible, and hence the appearance quality is inferior. Further, the strength and rigidity are decreased, and hence the durability is deteriorated concerning the function of the weak portion for the air bag.
In the case of the technical concept disclosed in Japanese Laid-Open Patent Publication No. 8-282420 concerning the conventional technique described above, the following inconvenience arises. That is, a considerable burden is imposed on the investment for the equipment, because it is necessary to use the expensive sensor for sensing the laser. Further, the control of the laser beam is complicated in order to obtain a constant thickness of the weak portion for the air bag.
In the case of the technical concept disclosed in Japanese Laid-Open Patent Publication No. 10-85966 concerning the conventional technique described above, the following inconvenience arises. That is, the arrangement of the control unit is complicated, and the production cost is expensive, because a method is adopted, in which the comparison is made for the correlative reference value concerning the residual strength and the integral value obtained with a detection signal.
A general object of the present invention is to provide a perforating machining method based on a laser beam, which makes it possible to reduce the diameter of a through-hole bored by means of a convenient method without requiring any excessive equipment investment.
A principal object of the present invention is to provide a perforating machining method based on a laser beam, which makes it possible to reduce the diameter of a through-hole bored through a weak portion for an air bag by means of a convenient method without requiring any excessive equipment investment.
Another object of the present invention is to provide a perforating machining method based on a laser beam, which makes it possible to form a weak portion for an air bag having such an appearance quality that a through-hole bored by the laser beam is invisible, in which the durability is realized for the function.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.